Process and apparatus for the vapor deposition of metals



Aug. 14, 1962 G. H. KESLER 3,049,440

PROCESS AND APPARATUS FOR THE VAPOR DEPOSITION OF METALS Filed July 28, 1959 .1 bull in INVENTOR v George H. Kesler CLZL TTORNEY United States Patent C) 3,049,440 PROCESS AND APPARATUS FOR THE VAPO DEPOSITION F METALS George H. Kesler, Worthington, Ohio, assignor, by

mesne assignments, to Chilean Nitrate Sales Corporation, New York, N.Y., a corporation of New York Filed July 28, 1959, Ser. No. 830,028 7 Claims. (Cl. 117107) This invention relates, in general, to an improved process for the production of high-purity metals by reaction or decomposition of a compound of the metal in contact with a heated deposition surface. In particular, the invention involves the provision of a unique method for introducing the reactant or reactants into contact with a deposition surface of the general class defined so as to promote a more uniform and dense deposit of the desired metal on said surface. The invention further involves the provision of novel apparatus for elfectuating the foregoing objectives.

It has been firmly established heretofore that a number of metals may be produced in a high state of purity by a process involving vapor deposition techniques. Briefly, this process entails the formation of the metal by chemical reaction at a heated surface, as, for example, a resistively-heated filament, or an inductively heated rod, or an indirectly heated deposition sheath. One of the principal examples of such vapor-deposition techniques is the so-called van Arkel-de Boer process for the production of titanium, chromium, hafnium, zirconium, thorium, etc., by decomposition of a corresponding iodide of the metal in contact with a resistively-heated filament of the same metal, or a different metal such as tungsten or molybdenum (Van Arkel, A. E., and de Boer, LH.) Preparation of Pure Titanium, Zirconium, lHafnium, and Thorium Meta Z. Anorg. U. Allgem. Chem, 148, pp. 345-350, 1950, U.S. Patents Nos. 2,694,662; 2, 694,653 and 2,694,654 to A. C. Loonam).

In order to render these processes sufficiently efficient and productive for commercial operations, it is advantageous to employ forced convection or similar dynamic flow of the iodide feed into contact with the dissociationdeposition element (see also U.S. Patent No. 2,895,852

to A. C. Loonam). On the other hand, when forced convection feeding is employed under such conditions as to achieve optimum high deposition rates, the metallic deposits produced are generally highly irregular, spiny structures having relatively poor mechanical strength. As a result, the filament carriers for the metal deposits, if permitted to grow to a diameter much in excess of one inch, will usually fail under their own weight at the high temperatures involved. Alternatively, in the case of the resistively-heated filaments, the irregular nature of the metallic deposits renders it extremely diflicult to maintain uniform electrical operating characteristics. This type of filament failure has received considerable attention, since it represents a most serious drawback to the commercial application of the vapor-deposition processes, and particularly the van Arkel-de Boer process, but, for the most part, prior attempts at overcoming the problem have been centered around changes in the filament or deposition surface, per se.

'Heretofore, the reactants utilized in vapor-deposition units have been introduced at one end of a vessel containing one or more filaments, and the reaction products together with any unchanged reactants are withdrawn at the opposite end of the vessel. Under these conditions, my investigations have demonstrated that a non-uniform velocity distribution in the region of the filaments is inevitable. As a result, the metallic deposits themselves are irregular, showing non-uniform deposition along their lengths, and containing local fissures which tend to entrap and retain reaction products such that the metal is not of the purity desired. Most significantly, however, as pointed out hereinbefore, such deposits possess decidedly inferior physical properties resulting in frequent filament failure.

The process and apparatus of the present invention provide for the attainment of more dense, uniform products having superior physical properties and purity, through the expedient of introducing the vapor-state reactant into the deposition vessel under such conditions that a substantially uniform velocity distribution profile is obtained. Thus, I have found that by introducing the feed material in the form of a jet stream at a point between the lowest level of the deposition elements and the vapor exit with the stream being maintained at a substantially higher velocity than the net axial velocity prevailing in the deposition chamber in the direction of the vapor outlet, more uniform expansion of the feed into the deposition chamber and circulation of the vapor stream within the chamber is realized, and a resultant more uniform velocity distribution is achieved.

It is believed that the invention may be best understood by reference to the following detailed description of one embodiment of the same taken in conjunction with the accompanying drawing wherein the single figure is a crosssectional elevational view of a deposition furnace incorporating the dynamic feed principles of the invention.

With reference to the drawing, there is shown a substantially cylindrical deposition chamber formed of an outside metallic shell 11 fitted with a liner 12 of any suitable iodine-iodide resistant insulating material, such as molybdenum radiation shields. The deposition chamber is provided with a top closure plate 13 adapted to seal the chamber against the ingress and egress of gases, but removable therefrom for purposes of recovering the metal output of the unit. Suspended downwardly into the deposition chamber from closure plate 13 are a plurality of directly-heated U-shaped resistance filaments 14, three being shown in the drawing, which are adapted to be connected to an electrical power supply (not shown) at contact terminals 15 projecting through the closure plate 13 to the outside of the deposition chamber. The bottom of the deposition chamber is fitted with an outlet duct 16 communicating with the inside of the chamber through a suitable outlet orifice 17. Directly below the outlet orifice 17, within the outlet duct 16, there is positioned a suitable outlet bafile 18. The outlet duct 16, in turn, communicates through an upwardly directed right angle extension 19 with an exit port 20 adapted to be connected to any suitable vacuum equipment (not shown) for outgassing the unit, and for directing the =by-products of the primary deposition reaction to secondary treatment units.

Approximately mid-way between the lowermost level of the suspended deposition filaments 14 and the outlet orifice 17 of the deposition chamber, there is positioned an inlet nozzle 21, directed radially inwardly along a diameter of the chamber. It is found that this precise positioning of the inlet nozzle in combination with the radial direction of the vapor stream entering the deposition chamber through 0 unit for pressure readings. High-pressure tap 23 is located approximately midway between the top and bottom of the deposition vessel, and directly above the position of the radial inlet nozzle 21. This position corresponds to an approximate average bulb pressure, in that readings at this point are not affected by high-impact pressures which might arise as a result of the jet vapor feed through nozzle 21. Tap 22 is a low-pressure tap and is located in the top of exit duct 16 at a point removed from the outlet orifice 17.

While the apparatus illustrated in the drawing was designed specifically to promote a more uniform deposit of titanium by the thermal decomposition of titanium tetraiodide, it will be readily appreciated that the uniform velocity distribution achieved through use of this feed technique is equally applicable to the deposition of other metals via the decomposition mechanism, or by reduction of their compounds with appropriate reducing agents. In addition, the invention may be practiced in conjunction with either single or multiple deposition elements, and with deposition elements of various shapes and configuration. The deposition elements may be heated by any of the conventional methods, and the invention is not limited to use in connection with resistively-heated filaments of the type illustrated in the drawing.

The following example will further serve to illustrate a typical application of the basic principles of my invention to the production of titanium within a deposition unit of the type illustrated within the drawing.

Example A deposition chamber measuring 15.5 inches ID. by 24.5 inches in height is joined to an outlet duct of approximately 45 inches in height. The bottom of the vessel is fitted with a circular outlet orifice measuring 12.8

inches in diameter, and a circular outlet baffie of 12.8

0.26 inch in diameter, is positioned 5 inches above the bottom of the deposition chamber.

The foregoing bulb when operated with Til. at weight flow rates to the inlet nozzle ranging from 0.026 to 0.061

pounds/second is capable of providing highly uniform W velocity distribution, with resulting smooth, dense titanium deposits on the filaments.

Having thus described the subject matter of my invention, what it is desired to secure by Letters Patent is:

1. Process for the vapor deposition of metals that;

comprises, reacting a compound :of the metal by contacting the same in its vapor state with a heated surface maintained within a closed reaction vessel to promote the continuous formation and deposition of said metal in elemental form on said surface, removing gaseous prodnets of the reaction and unreacted quantities of said metal compound from said vessel through an outlet port positioned in the bottom of the vessel at a point removed from the lowermost portion of said heated deposition surface, and establishing and maintaining uniform velocity distribution of said vapor state metal compound in contact with the heated deposition surface to promote the formation of a uniform, dense deposit of said metal thereon by introducing the metal compound into said reaction vessel in the form of a radial pressure stream at a point intermediate the lowermost portion of said heated deposition surface and said outlet port, and in a direction substantially normal to a plane extending from the lowermost portion of said surface to said outlet port.

2. The process as claimed in claim 1, wherein said stream of metal compound vapor is maintained at a substantially higher velocity than the net axial velocity prevailing within said reaction vessel in the direction of said outlet port.

3. The process as claimed in claim 1, wherein said metal compound consists of an iodide of the metal which is thermally decomposed in contact with said heated surface to effect deposition of the metal thereon with liberation of elemental iodine.

4. The process as claimed in claim 1, wherein said metal compound is titanium tetraiodide which is thermally decomposed in contact with said heated surface to effect deposition of titanium thereon with liberation of elemental iodine.

5. The process as claimed in claim 1, wherein said heated deposition surface consists of a plurality of resistively-heated filaments extending in spaced relationship from the top of said reaction vessel to a point above the point of introduction of said vapor stream into said reaction vessel, said stream being introduced into the reaction vessel in a direction substantially parallel to a plane extending through the lowermost portions of said filaments.

6. Apparatus for the vapor deposition of metals from compounds of the metals that comprises, a substantially closed reaction vessel, at least one heated deposition surface positioned within said reaction vessel and adapted on contact with vapors of a metal compound introduced therein to promote chemical reaction of said compound and deposition of the metal of the compound onto said surface, an outlet port positioned in the bottom of said reaction vessel at a point removed from the lowermost portion of said heated deposition surface for removing reaction gases and unreacted quantities of said metal compound from the vessel, and an inlet nozzle positioned intermediate the lowermost portion of said heated deposition surface and said outlet port and adapted to introduce into said vessel vapors of said metal compound in the form of a radial pressure stream in a direction substantially normal to a plane extending from the lowermost portion of said deposition surface to said outlet port.

7. Apparatus for the vapor deposition of metals from compounds of the metals that comprises, a substantially closed tubular reaction vessel, a plurality of resistivelyheated filaments extending in axial, spaced relationship into said reaction vessel from the top thereof and adapted on contact with vapors of a metal compound introduced therein to promote chemical reaction of said compound and deposition of the metal of the compound onto said filaments, an outlet port positioned in the bottom of said reaction vessel at a point removed from the lowermost tips of said filaments for removing reaction gases and unreacted quantities of said meal compound from the vessel, and an inlet nozzle positioned in the sidewall of said vessel intermediate the lowermost tips of said filaments and said outlet port and adapted to introduce into said vessel vapors of said metal compound in the form of a pressure stream in a direction substantially normal to the axis of said tubular vessel.

References Cited in the file of this patent UNITED STATES PATENTS 2,539,149 Miller Ian. 23, 1951 2,636,855 Schwarz Apr. 28, 1953 2,694,652 Loonam Nov. 16, 1954 2,694,653 Loonam Nov. 16, 1954 2,694,654 Loonam Nov. 16, 1954 2,719,093 Voris Sept. 27, 1955 2,739,566 Shapiro et al Mar. 27, 1956 2,820,722 Fletcher Jan. 21, 1958 2,895,852 Loonam July 21, 1959 

1. PROCESS FOR THE VAPOR DEPOSITION OF METALS THAT COMPRISES, REACTING A COMPOUND OF THE METAL BY CONTACTING THE SAME IN ITS VAPOR STATE WITH A HEATED SURFACE MAINTAINED WITHIN A CLOSED REACTION VESSEL TO PROMOTE THE CONTINUOUS FORMATION AND DEPOSITION OF SAID METAL IN ELEMENTAL FORM ON SAID SURFACE, REMOVING GASEOUS PRODUCTS OF THE REACTION AND UNREACTED QUANTITIES OF SAID METAL COMPOUND FROM SAID VESSEL THROUGH AN OUTLET PORT POSITIONED IN THE BOTTOM OF THE VESSEL AT A POINT REMOVED FROM THE LOWERMOST PORTION OF SAID HEATED DEPOSITION SURFACE, AND ESTABLISHING AND MAINTAINING UNIFORM VELOCITY DISTRIBUTION OF SAID VAPOR STATE METAL COMPOUND IN CONTACT WITH THE HEATED DEPOSITION SURFACE TO PROMOTE THE FORMATION OF A UNIFORM, DENSE DEPOSIT OF SAID METAL THEREON BY INTRODUCING THE METAL COMPOUND INTO SAID REACTION VESSEL IN THE FORM OF A RADIAL PRESSURE STREAM AT A POINT INTERMEDIATE THE LOWERMOST PORTION OF SAID HEATED DEPOSITION SURFACE AND SAID OUTLET PORT, AND IN A DIRECTION SUBSTANTIALLY NORMAL TO A PLANE EXTENDING FROM THE LOWERMOST PORTION OF SAID SURFACE TO SAID OUTLET PORT. 